Fractional Crystallization Kinetics and Formationof Metastable β‑Form Homocrystals in Poly(l‑lacticacid)/Poly(d‑lactic acid) Racemic Blends Induced byPrecedingly Formed Stereocomplexes

Stereocomplex (SC) crystallization has been an effective way to improve the physical performance of polymer materials. However, SC crystallization of stereocomplexable polymer blends with complementary configurations is much more complicated than the conventional homocrystallization because of the interplay and competition between SC and homo crystallizations. Herein, we used the poly(l-lactic acid)/poly(d-lactic acid) (PLLA/PDLA) racemic mixture as the stereocomplexable blend and investigated its crystallization kinetics, polymorphic structure, lamellae structure, and crystalline phase transition. Unexpectedly, the medium-molecular-weight (MMW, ∼40k) PLLA/PDLA racemic blend exhibits unique fractional crystallization kinetics (i.e., multiple crystallization peaks) during heating because of the constrained effect of the precedingly formed SCs in the early stage of crystallization. The MMW PLLA/PDLA blend forms the metastable β-form homocrystals (HCs) at a low crystallization temperature (Tc, 75–100 °C) but...